1. Field of the Invention
The present invention relates to a thermally-assisted magnetic recording head fabricated by joining a slider and a light source unit that includes a light source, and further relates to a method for manufacturing the thermally-assisted magnetic recording head.
2. Description of the Related Art
As the recording densities of magnetic recording apparatuses become higher, as represented by magnetic disk apparatuses, further improvement has been required in the performance of thin-film magnetic heads and magnetic recording media. As the thin-film magnetic heads, a composite-type thin-film magnetic head is widely used, which has a stacked structure of a magnetoresistive (MR) element for reading data and an electromagnetic transducer for writing data.
Whereas, the magnetic recording medium is generally a kind of discontinuous body of magnetic grains gathered together, and each of the magnetic grains has a single magnetic domain structure. Here, one record bit consists of a plurality of the magnetic grains. Therefore, in order to improve the recording density, it is necessary to decrease the size of the magnetic grains and reduce irregularity in the boundary of the record bit. However, the decrease in size of the magnetic grains raises a problem of degradation in thermal stability of the magnetization due to the decrease in volume.
As a measure against the thermal stability problem, it may be possible to increase the magnetic anisotropy energy KU of the magnetic grains. However, the increase in energy KU causes the increase in anisotropic magnetic field (coercive force) of the magnetic recording medium. Whereas, the intensity of write field generated from the thin-film magnetic head is limited almost by the amount of saturation magnetic flux density of the soft-magnetic material of which the magnetic core of the head is formed. As a result, the head cannot write data to the magnetic recording medium when the anisotropic magnetic field of the medium exceeds the write field limit.
Recently, as a method for solving the problem of thermal stability, so-called a thermally-assisted magnetic recording technique is proposed. In the technique, a magnetic recording medium formed of a magnetic material with a large energy KU is used so as to stabilize the magnetization, then anisotropic magnetic field of a portion of the medium, where data is to be written, is reduced by heating the portion; just after that, writing is performed by applying write field to the heated portion.
In this thermally-assisted magnetic recording technique, there has been generally used a method in which a magnetic recording medium is irradiated and thus heated with a light such as near-field light (NF-light). In this case, it is significantly important to stably supply a light with a sufficiently high intensity at a desired position on the magnetic recording medium. However, from the beginning, more significant problem to be solved exists in where and how a light source with a sufficiently high output of light should be disposed inside a head.
As for the setting of the light source, for example, U.S. Pat. No. 7,538,978 B2 discloses a configuration in which a laser unit including a laser diode is mounted on the back surface of a slider, and US Patent Publication No. 2008/0056073 A1 discloses a configuration in which a structure of a laser diode element with a monolithically integrated reflection mirror is mounted on the back surface of a slider. Further, US Patent Publication No. 2005/0213436 A1 discloses a structure of slider that is formed together with a semiconductor laser, and Robert E. Rottmayer et al. “Heat-Assisted Magnetic Recording” IEEE TRANSACTIONS ON MAGNETICS, Vol. 42, No. 10, p. 2417-2421 (2006) discloses a configuration in which a diffraction grating is irradiated with a light generated from a laser unit provided within a drive apparatus.
As described above, various types of the setting of the light source are suggested. However, the present inventors propose a thermally-assisted magnetic recording head with a “composite slider structure” which is constituted by joining a light source unit provided with a light source to the end surface (back surface) of a slider provided with a write head element, the end surface being opposite to the opposed-to-medium surface of the slider. The “composite slider structure” is disclosed in, for example, US Patent Publication No. 2008/043360 A1 and US Patent Publication No. 2009/052078 A1.
In fabrication of a thermally-assisted magnetic recording head having such a “composite slider structure”, it is significantly important to accurately align the light source unit with the slider when joining them together.
In practice, the head need to be fabricated in such a way that light emitted from the light-emitting center located in the light-emitting surface of the light source is reliably allowed to be incident exactly at the light-receiving end of an optical system such as a waveguide located on the back surface of the slider, in order to provide a sufficiently high light use efficiency. To this end, the light-emitting center and the light-receiving end are aligned with each other in the track width direction and in the direction perpendicular to the track width direction as accurately as possible. Typically, it is preferable that the accuracy of the alignment be within ±1 μm (micrometer) in actual manufacturing.
One approach to achieving such high alignment accuracy is active alignment. In the active alignment, a light source such as a laser diode is actually being activated while the light source and the optical system are moved relative to each other, light emitted from the light source and incident at the light-receiving end of the optical system is monitored on the light-emitting end side of the optical system in real time, and a monitoring position at which the highest light intensity is obtained is set as the desired relative position of the light source and the optical system. However, the active alignment is a method of merely locating a two-dimensional optimum position and has the drawback of requiring a considerably long time for alignment. In addition, power supply probes need to be applied to the electrodes of the light source in order to keep activating the light source during the alignment, which further increase the time required for the alignment. Furthermore, a head structure and probing facilities which are required for the probing increase the manufacturing load.
There is another approach called passive alignment. In the passive alignment, a light source and an optical system are physically coupled to each other or are moved through image recognition, thus to align them with each other using an existing groove, an existing projection, or a marker provided in the light source and/or the optical system as a mark for alignment. In general, the passive alignment takes a shorter time than the active alignment. As an example of passive alignment, Japanese Patent Publication No. 2003-142892A discloses a method in which a recognition marker of the first joint object on the upper surface side and a recognition marker of the second joint object are aligned by using the positional relation of the recognition marker of the first joint object on the upper surface side with a recognition marker on the lower surface side or a contour of the first joint object. In the alignment of this method, a dual-field-of-view recognition means is required to be inserted between the first joint object and the second joint object.
Since the passive alignment uses such a recognition means which is, for example, inserted or drawn out, and since the added markers may have a positional error, the accuracy of the passive alignment tends to be low compared with the active alignment. In addition, it is considerably difficult to find or add a marker for the passive alignment on the light-source unit during fabrication of a head having the “composite slider structure”. Further, it is also difficult to perform an alignment with use of a contour of the joint object. In fact, since processing accuracy, that is dimensional accuracy of the contour, is, for example, approximately ±5 μm, it is difficult to secure alignment accuracy within ±1 μm by using the positions of the contour as a standard.
As understood from the above descriptions, there is a need for a novel alignment method capable of aligning a light source unit and a slider with each other with a sufficiently high alignment accuracy in a short processing time due to simplified processes, in fabrication of a thermally-assisted magnetic recording head having a “composite slider structure”.